Go to https://www.researchgate.net/requests to find the requests to your papers. At that place you will be able to reply by sending the full text or by denying the request.

I think you can send a full text article manually or researchgate update it automatically

To publish your research findings on ResearchGate, navigate to your profile page and click the "Add new" button. Then, select "Published research" and choose the appropriate publication type. Fill in the details of your research, including title, authors, and publication date, and upload the full text if you have the rights to do so. You can also add preprints or other types of research using the same "Add new" button.

Select I have the full-text and you will have the option to add a public full-text, or to send a full-text in a private message. If you select No full-text to share, you can choose to send a message to the researcher who requested the full-text from you.Updates inform you about new followers, your publications that have been added by your co-authors, answers to questions you asked or followed, and much more. You can find your updates by clicking on the bell icon at the top-right of any ResearchGate page. Clicking on a specific update takes you to the new content, so you can see who’s interacting with your research and how.

Messages is where you can find private messages you’ve received or sent. You can find your messages by clicking on the envelope icon on the top-right of any ResearchGate page.

Requests contains all Full-text, Author, and other types of requests. These generally require some kind of answer or confirmation. You can find your requests by clicking on the speech bubble icon at the top-right of any ResearchGate page.