Why can't I activate my Google Merchant Center account with my phone number?

Google needs a valid business phone number to activate my Merchant Center account. I input right mobile number to receive otp, but the following error occurred “An unknown error occurred. Try again later, or contact support.”

seeking your kind support.

As this is a technical issue, the only way to resolve this is by reaching Google via the dedicated support system here: https://support.google.com/merchants/contact/shopify_3p_support_app