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It seems like the issue you're experiencing with the Cognitive Services endpoint {Endpoint}/vision/v3.1/read/analyze is indeed related to the limitations of the F0 (free) pricing tier. The F0 tier has certain restrictions, including the number of pages it can process in a document. you can consider upgrading to the S0 (standard) pricing tier, which offers more capabilities and fewer limitations. This should allow you to process more pages in your PDF documents. Here's a summary of the key differences between the F0 and S0 tiers:
F0 (Free) Tier: Limited to processing a smaller number of pages and transactions per month.
S0 (Standard) Tier: Allows for processing more pages and offers higher transaction limits.
Thankyou!