Allow x-framing of secure checkout page in Woocommerce

I am trying to allow a call center to x-frame the store below so they can process customer orders using their system. The checkout page loads blank currently due I believe to x-framing being forbidden as default (with the header set for x-framing to DENY).

I believe the best option is potentially to allow the call centre’s IP addresses to x-frame the site (and the secure checkout page) but using ALLOW-FROM xxx doesn’t seem to work with IP addresses (only domains) and results in a server error.

Has anyone else been able to to x-frame their woocommerce store, especially to allow call centres to integration with it?

Store – https://www.bodymassageshop.com