Third Party Calling Provider Integration Issue in Hubspot - Unhandled Promise Rejection TypeError: this.handleSetCallProvider is not a function

Question

We have developed a third-party calling connector for Hubpot. It's working fine in a development environment. However, we are facing issues in making the app production-ready. We have completed the following steps.

1. Created an app.
2. Send the API request for adding the app to the account.
3. We can see our app in the connected app tab in our account.

When we go to the contact page to load over calling provider, we get the following error in browser logs.

index.js:54 Unhandled Promise Rejection TypeError: this.handleSetCallProvider is not a function
at handleSelectToNumber (CallProviderViewport.js:385:14)
at handleTriggerCallingEvent.ts:13:67
at index.js:3912:58
at index.js:1384:16
at Ye.iterate.Je.iterate (index.js:1733:11)
at We.__iterate (index.js:1382:32)
at In.__iterate (index.js:3912:24)
at In.forEach (index.js:4388:19)
at Object.Gi [as triggerEvent] (handleTriggerCallingEvent.ts:13:53)
at ys (triggerHostMessageOpenWidget.ts:4:22)
at Ss (handleOpenWidget.ts:19:3)
at o (hsCallingUtils.ts:17:13)
at hsCallingUtils.ts:26:7
at new Promise (<anonymous>)
at l (hsCallingUtils.ts:24:10)
at p (openCallingWidget.ts:79:10)
at CallingOnboarding.tsx:115:5
at onClick (UILink.js:98:22)
at Object.Ke (react-dom.production.min.js:52:317)
at Ze (react-dom.production.min.js:52:471)
at et (react-dom.production.min.js:53:35)
at Lr (react-dom.production.min.js:100:68)
at Ur (react-dom.production.min.js:101:380)
at react-dom.production.min.js:113:65
at Ue (react-dom.production.min.js:292:189)
at He (react-dom.production.min.js:50:57)
at $r (react-dom.production.min.js:105:469)
at cn (react-dom.production.min.js:75:265)
at ln (react-dom.production.min.js:74:124)
at t.unstable_runWithPriority (scheduler.production.min.js:18:343)
at oi (react-dom.production.min.js:122:325)
at De (react-dom.production.min.js:292:48)
at un (react-dom.production.min.js:73:352)
at HTMLDivElement.o (index.js:412:1)

We are following the steps given in this guide.