The general rule, even without knowledge of the law, is that debts must be satisfied in the soonest time, and follow the agreed-upon terms and conditions between sa nagpautang and sa nangutang. Mahirap kasing maningil talaga, kasi nagkakahiyaan pa when it comes to payment.
Pero make sure, as the nangutang, na talagang wala kang pambayad. If there are posts in FB that may suggest otherwise, baka naman yun yung trigger na nagcause nung nagpautang na magrant sa FB and nai-post pa yung pangalan mo. Frustration on the part of the nagpautang yun, plain and simple.
Things can be repaired. Try to pay the debt in the soonest time, and have your friend post in FB that you have satisfied your debt and apologize on the said post for any reputational harm that came in your way. Of course, this is not a perfect compromise, but it is a good way to avoid this matter from escalating further.
Good luck. May the force be with you!