I am a G Suite Reseller and I need to create a website where my clients can enter the number of g suite users/licenses they want to add and it will calculate the price for them based on the number of licenses and the remaining period.
I have already searched the reseller API page but didn't find any useful resources.
I don't think you need the re-seller API for that, you can check the G Suite licenses price at gsuite.google.com you can just create your own page and calculate it based on those prices,the re-seller API works just to manage the subscription of your clients but nothing related to billing all the reference about the reseller API can be found here https://developers.google.com/admin-sdk/reseller/v1/reference/.
Now if you want to retrieve the expiration date for the plan then you can use the Rseller API,Reseller API > Subscriptions you will find the JSON with the plan start and end time, I would say you can use them to .
"plan": { "planName": string, "isCommitmentPlan": boolean, "commitmentInterval": { "startTime": long, "endTime": long }
I don't have a reseller account but I would say that the best option is to use the Subscriptions > Get to retreive the start and endtime from the plan. The methods I found are
What I am not sure since I dont have how to test is if these two are linked to an annual plan or can be used to any other plan. I hope this information can be of help, greetings.