It's so hard to find a reliable freelancer, I need help connecting to the Gmail API to pull files from users' emails every day

Need help APIs
1

I started to build invoices CRM saas, the system need to pull files from users Gmail daily and process them with OCR API to get invoices information.
I started to set up the Gmail API but I struggling to get the access token and the refresh token.
Also i struggling in get the file with the api.
Looking for reliable help!