Hi Zyril,
The device supports three encoding formats for certificates and private keys: DER, PEM, and PKCS12. It is recommended that the CA provide certificates and private key files in the three encoding formats. Certificates and private key files in other formats need to be converted before being imported.
The common suffixes for DER encoding (ASCII) are .DER, .CER, and .CRT.
The common PEM encoding (Base64) suffixes are .PEM, .CER, and .CRT.
The common suffixes of PKCS12 encoding are .P12 and .PFX.
Please try to download the certificate again and import it to the device.
Please refer to:
https://support.huawei.com/hedex/hdx.do?docid=EDOC1100064350&id=dc_cfg_nac_2004u_1&lang=enI hope it helps!