If your vehicle is showing seatbelt is stuck in the buckle and won't release, here are the most likely causes and the parts you'll need to fix each one.
Small items like coins, food crumbs, or small toys can fall into the buckle slot and physically block the internal release mechanism from disengaging.
Spilled beverages like soda or coffee can seep into the buckle mechanism and dry into a sticky residue, effectively gluing the release latch and button shut.
The internal return spring or plastic latch mechanism inside the buckle has broken or worn out from repeated use, preventing it from releasing the metal latch plate.
If the seats or interior trim were recently removed, the seatbelt may have been routed incorrectly or twisted during reinstallation, causing the latch plate to wedge tightly and bind inside the buckle.
If the vehicle was recently in a collision, the explosive pretensioner built into the buckle may have deployed, permanently locking the seatbelt to secure the occupant.