What they had hoped would be a milestone on the path back to normal life became the start of a bureaucratic nightmare.
One year on, it shows no sign of ending for them, their newly born son or for many other refugees from Syria, whose misery at losing their homes has been compounded by a new fear they may never be able to return.
It is a dilemma with knock-on effects for stability in Lebanon, sheltering more than a million Syrian refugees, and potentially for other countries in the Middle East and Europe they may flee to if tension spills over.
After they had agreed their union with the sheikh in the insulated tent that had become home to Khadija's family, the newlyweds both spent months digging potatoes in the Bekaa valley, one of Lebanon's poorest districts, to make ends meet.
Only after they had a baby boy, Khalaf, did they realise the wedding had been a mistake.
When the couple went to register his birth at the local registry, they were told they could not because they had no official marriage certificate.
Without registration, Khalaf is not entitled to a Syrian passport or other ID enabling him to go there. Without proper paperwork, he also risks future detention in Lebanon.
Asked why they did not get married by an approved religious authority, Ammar and Khadija looked at each other before answering: "We didn't know."
Laws and legislation seem very remote from the informal settlements in the northern Bekaa Valley, where Syrian refugee tents sit on the rocky ground amongst rural tobacco fields. Marriages by unregistered sheikhs are common but hard to quantify because authorities often never hear of them.
For whereas in Syria, verbal tribal or religious marriages are easy to register, Lebanon has complex and costly procedures.
You first need to be married by a sheikh approved by one of the various religious courts that deal with family matters, who gives you a contract. Then you have to get a marriage certificate from a local notary, transfer it to the local civil registry and register it at the Foreigners' Registry.
Most Syrians do not complete the process, as it requires legal residency in the country, which must be renewed annually and costs $200, although the fee was waived for some refugees this year. Now they have had a child, Ammar and Khadija also need to go through an expensive court case.
The casual work Ammar depends on -- picking potatoes, onions or cucumbers in five hour shifts starting at 6 am -- pays 6,000 LBP ($4) a day, not enough to live on, let alone put aside.
"One bag of diapers costs 10,000 liras," he said.
Sally Abi Khalil, Country Director in Lebanon for UK-based charity Oxfam, said 80 percent of Syrian refugees do not have valid residency, one of the main reasons why they do not register their marriages, alongside the issue of the sheikhs.
"Babies born to couples who didn't register their marriage risk becoming stateless," she said.
Refugees can only legally make money if they have a work permit, which requires legal residency, a Catch 22 situation partially tackled in February when the fee was waived for those registered with the UNHCR prior to 2015 and without a previous Lebanese sponsor.
Lebanon's Directorate General of Personal Status took another step to help the refugees on September 12, when it issued a memo which waived the parents' and child's residency prerequisite for birth registration, it said.
But if you are married by an unauthorised sheikh, which includes all Syrian sheikhs, the process is more complicated, made worse by a clock ticking over the fate of your offspring, whose birth has to be registered within a year.
"In registering marriages, the biggest problem we faced was the sheikh," said Rajeh, a Syrian refugee, speaking for his community in a village in southern Lebanon. "In Syria, the child would be ten years old and you can register him in one day."
If the one-year deadline is missed in Lebanon, parents have to open a civil court case estimated to cost more than one hundred dollars and still requiring legal residency, which Ammar and Khadija, who met in the informal settlement, do not have.
Legal residency becomes a requirement in Lebanon at the age of 15. At that point, many Syrians pull their children from school and do not let them stray far from the house or neighbourhood for fear they will be stopped and detained.
More than half of those who escaped the Syrian conflict that began in 2011 are under 18 years old, and around one in six are babies and toddlers, said Tina Gewis, a legal specialist from the Norwegian Refugee Council.
Politicians pressured by some Lebanese saying the country has carried too much of the burden of the refugee crisis are pushing harder for the return of the displaced to Syria, raising the stakes since documentation is required for repatriation.
If they have used an unauthorised sheikh, couples are encouraged to redo their marriages, said Sheikh Wassim Yousef al-Falah, Beirut's sharia (Islamic law) judge, who said the court's case load had tripled with the influx of Syrian refugees.
But that is not an option for Ammar and Khadija because a pregnancy or the birth of a child rules that option out.
Gewis said that in any case new marriages risked complicating future inheritance or other legal issues and costs were prohibitive, with courts charging up to $110 to register even straightforward marriages by an approved sheikh.
Ziad al Sayegh, a senior advisor in Lebanon's newly-formed Ministry of State for Displaced Affairs said Beirut was keen to help the refugees overcome their difficulties.
"We don't want them to be stateless, because if you're stateless you have a legal problem that will affect the child and affect the host country," he said.
(Editing by Philippa Fletcher)
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