You need to go use message store APIs to get the full details of your message.
First search for the messages using Get Message List API : https://developers.ringcentral.com/api-reference/Message-Store/listMessages
You will get all the sms messages list using the API. You need to give From date and To date when you are searching the messages.
example below:
https://platform.devtest.ringcentral.com/restapi/v1.0/account/~/extension/~/message-store?dateFrom=2020-01-01&dateTo=2020-09-01&page=1&perPage=100
You can see dateFrom=2020-08-01 and dateTo=2020-09-01 and it will list all the messages within this period.
Each message that will listed there will have a message id and an attachment id along with subject as you message content:
To get the message content of specific message, you can use that message id and attachment id in Get Message Content API here: https://developers.ringcentral.com/api-reference/Message-Store/readMessageContent
and you need to put that message id number and attachment number you got from there in the API to get the message content .
https://platform.devtest.ringcentral.com/restapi/v1.0/account/~/extension/~/message-store/<message id> /content/<attachment id>?contentDisposition=Inline
example:
https://platform.devtest.ringcentral.com/restapi/v1.0/account/~/extension/~/message-store/8419061004/content/8419061004?contentDisposition=Inline
I am missing messages regarding Ringcentral app. I last accessed them in December. Please contact me at (708) 429-0375 to help retrieve my messages.