I will develop a bitcoin wallet with PHP

https://www.bitcoin.com/get-started/how-bitcoin-transactions-work/

https://en.bitcoin.it/wiki/Block

https://developer.bitcoin.org/devguide/block_chain.html

https://statoshi.info/d/000000017/fee-estimates?orgId=1

https://en.bitcoin.it/wiki/Miner_fees#Fee_Plotting_Sites

https://bitcointalk.org/index.php?topic=81626.20

https://en.bitcoin.it/wiki/PHP_developer_intro

https://github.com/cryptoapi/Payment-Gateway

https://developer.bitcoin.org/examples/testing.html

https://github.com/dryphp/bitcoin.php/blob/master/src/bitcoin.inc

https://wiki.uniformserver.com/index.php/SSL_PHP_Server_Key_and_Certificate_generation

https://www.ellipal.com/blogs/support/calculate-bitcoin-miners-fee

https://bitcoinops.org/en/tools/calc-size/

https://news.bitcoin.com/how-to-calculate-bitcoin-transaction-fees-when-youre-in-a-hurry/