Unable to create a Merchant ID Certificate from an ECC 256 certificate signing request

Please follow the following steps and important step is the "Let me specify the key pair information".

If you miss that then you wont get the cert which you are looking for.

Within the Keychain Access drop down menu, select Keychain Access > Certificate Assistant > Request a Certificate from a Certificate Authority.

• In the Certificate Information window, enter the following information:
  • In the User Email Address field, enter your email address.
  • In the Common Name field, create a name for your private key (e.g., John Doe Dev Key).
  • The CA Email Address field should be left empty.
  • In the "Request is" group, select the "Saved to disk" option.
  • Select "Let me specify key pair information".
• Click Continue within Keychain Access and select the file location.
• Set the Key Pair Information to the following:
  • Algorithm: ECC
  • Key Size: 256 bits
• Click Continue within Keychain Access to complete the CSR generating process.

Update iOS 13

See this answer: CSR algorithm/size incorrect. Expected: RSA(2048)

I have changed file extension from certSigningRequest.certSigningRequest ◁ to ▶︎ certSigningRequest.csr and Its working fine for me.

@sagarvkotak Very helpful, I was using the Mac terminal to generate CSRs, using Keychain Access is more intuitive. So I'm integrating Apple Pay into a Shopify Store via headless ecomm that will flow into my visionOS app using Shopify's storefront API. Here's my rub, you cannot download the CSR file from Shopify bc this CSR file uses a ECC algorithm and 256 bits and Apple expects the RSA algo with 2048 bits. Therefore created the CSR via KeyChain Access and uploaded successfully to Apple Developer and downloaded the needed Merchant ID cert that then gets uploaded back into Shopify. Now every time I upload the Merchant ID cert into Shopify I get the below error. Any suggestions? Shopify doesn't have a clue how to resolve this issue. Thanks!