"PK algorithm tag" error with commercial certificate

Hello, I’m trying to use a commercial certificate with an project that uses mbedtls.
To debug the problem I’m using key_app from the programs/pkey folder.
After tweaking with MBEDTLS_MPI_MAX_SIZE I was able to get a significant error:

. Loading the public key … failed
! mbedtls_pk_parse_public_keyfile returned -0x3ae2
! Last error was: PK - The algorithm tag or value is invalid : ASN1 - ASN1 tag was of an unexpected value

I’ve tried to enable the weak ciphers to no use.

Any suggestion is greatly appreciated.

Kind regards,