The API keys are for individual use and are linked to your institution/organisation credentials. DO NOT SHARE THEM.
In the context of a literature review, which needs a low request rate and quota, you do not need a key to use the PubMed API.
If you want a higher request rate (about 10 requests/second instead of 3), you can optionally register a free NCBI API key from your NCBI account, under Account Settings → API Key Management. It remains entirely optional.
More info at: https://pmc.ncbi.nlm.nih.gov/tools/developers/
Some institutional Scopus subscriptions also require an institutional token (insttoken) in addition to the API key. If your API calls return an authentication error (HTTP 401) even with a valid key, contact Elsevier support to request an institutional token for your account. If your key works on its own, you do not need an institutional token.
Well done!
Now that you got your API keys, you can continue to the next tutorial → LitFetchR (Tutorial)