Hi @gael, i am new here and was trying to push patient record from postman to openmrs (OpenMRS Platform 2.4 with fhir module 1.3 and encountered the same issue as you did. I tailed my openmrs logs as i was trying to post and got the same error - " Column ‘uuid’ cannot be null"
I managed to get it working by including an id in all the key sections identifier, name, telecom, and address as @ibacher suggested above.
With some reverse engineering using a file of a patient i created from the openmrs gui, I managed to create the patient records in json to use in postman which would have all the key details for my openmrs system.
Hope this helps in someway.