Custom domain certificate creation with terraform fails with "InvalidCertificate: The certificate env-cert is invalid or password is incorrect."

I am trying to create a custom domain for a Container App using Terraform.

The issue I have is with the certificate.

I generated a set of fullchain.pem and privkey.pem using Certbot and Letsencrypt using certbot plugin for azure cloud for dns challenge.

Once generated created a cert.pfx using the following command:

openssl pkcs12 -inkey privkey.pem -in fullchain.pem -export -out cert.pfx

and also with the command that includes the certificate:

openssl pkcs12 -inkey privkey.pem -in fullchain.pem -certfile cert.pem -export -out cert.pfx

When applying the terraform plan, the resource "azurerm_container_app_environment_certificate" fails with the following error:
InvalidCertificate: The certificate env-cert is invalid or password is incorrect.

I verified that the password is correct by generating a certificate without password.

This is the resource declared in terraform:

resource "azurerm_container_app_environment_certificate" "env_cert" {
  certificate_blob_base64      = filebase64("certificates/cert.pfx")
  certificate_password         = var.cert_pass
  container_app_environment_id = azurerm_container_app_environment.app_env.id
  name                         = "env-cert"
}

I don't understand why the certificate format is invalid.