Failed to create certificate java.security.cert.CertificateException: Could not decode the client certificate

Question

I have this error:

System.CalloutException: Failed to create certificate java.security.cert.CertificateException: Could not decode the client certificate. Please ensure that it is a base64 representation of a PKCS12 file: toDerInputStream rejects tag type 45

I am integrating ADP into Salesforce using rest, I am trying to get access token from ADP.

Code - public class getAccessToken {

public static void getToken() {

    HttpRequest request = new HttpRequest();

    HttpResponse response = new HttpResponse();

    Http http = new Http();

    // Set the request URL

    String authEndpoint = 'https://accounts.adp.com/auth/oauth/v2/token';

    request.setEndpoint(authEndpoint);

    // Set the request method

    request.setMethod('POST');

    // Set the request headers

    request.setHeader('Content-Type', 'application/x-www-form-urlencoded');

    // Set the request body

    String payload = 'grant_type=client_credentials' +

        '&client_id=437134191f47' +

        '&client_secret=49651ff0-70b6baac';

    request.setBody(payload);

    // Retrieve the AFHMutualSSLCert key file from static resource

    StaticResource staticResourceAFHMutualSSLCert = [SELECT Body FROM StaticResource WHERE Name = 'AFHMutualSSLCert'];

    String AFHMutualSSLCertContent = staticResourceAFHMutualSSLCert.Body.toString();

    system.debug('AFHMutualSSLCertContent: '+AFHMutualSSLCertContent);

    // Convert the AFHMutualSSLCertContent key to Base64-encoded string

    Blob AFHMutualSSLCertKeyBlob = Blob.valueOf(AFHMutualSSLCertContent);

    String AFHMutualSSLCertKeyBase64 = EncodingUtil.base64Encode(AFHMutualSSLCertKeyBlob);

    system.debug('AFHMutualSSLCertKeyBase64: '+AFHMutualSSLCertKeyBase64);

    // Retrieve the private key file from static resource

    StaticResource staticResourcePrivateKey = [SELECT Body FROM StaticResource WHERE Name = 'AFHPrivateKey'];

    String privateKeyContent = staticResourcePrivateKey.Body.toString();

    system.debug('privateKeyContent: '+privateKeyContent);

    // Convert the private key to Base64-encoded string

    Blob privateKeyBlob = Blob.valueOf(privateKeyContent);

    String privateKeyBase64 = EncodingUtil.base64Encode(privateKeyBlob);

    system.debug('privateKeyBase64: '+privateKeyBase64);

     request.setClientCertificate(AFHMutualSSLCertKeyBase64, privateKeyBase64);

    system.debug('request: '+request.getBody());

    // Send the request and get the response

    response = http.send(request);

    system.debug('response: '+response);

    // Parse the response

    if (response.getStatusCode() == 200) {

        // Successful response

        Map<String, Object> responseMap = (Map<String, Object>) JSON.deserializeUntyped(response.getBody());

        String accessToken = (String) responseMap.get('access_token');

        System.debug('Access Token: ' + accessToken);

        // Use the access token for further API requests

    } else {

        // Error handling for failed request

        System.debug('Error: ' + response.getBody());

    }

}

}