Issue with Apple Pay Integration (Kashier Gateway) - Redirect URL Error

My WordPress site already accepts standard credit-card payments through the Kashier gateway (https://www.kashier.io/), but every Apple Pay attempt stalls with the message:
“redirect URL must be a valid url.”
The Return/Redirect URL is currently set inside the Kashier plugin settings, and I have not touched any other configuration. I need a quick dive into the plugin and, if necessary, the Kashier merchant dashboard to correct the URL scheme and clear the error.

What I expect:
• You locate the misconfigured URL or missing parameter.
• Apply the proper scheme so Apple Pay can finish its hand-off back to the site.
• Prove success with a completed Apple Pay transaction in live mode—no redirect error, funds captured.

Please share relevant experience with WordPress payment gateways—especially Apple Pay or Kashier—so I know you can move fast on this.