You are going to need a scanner capable of reading air bag codes or know someone who has one to see what the code is.
It could be an issue with the plug under the passenger seat since there is a weight sensing pressure pad in the seat to prevent the air bag from going off if a child seat is there. If that checks ok, that is where the scanner is going to come into play and a repair center. Messing with air bags isn’t something to take lightly since they can go off in your face while working on them.
Noticing the year of your truck, I’m guessing you are not from the US or Canada. Being that you have a truck in between the final year of the original Ranger and the current, new one. Where to post is a bit of a conundrum. Since your truck is closest to the 2019+ series of trucks, I think you did good.
Let us know what you find. Hopefully, it’s just a plug connection. Something nice and easy and cheap.