firstly, no software company is free forever. Serving you forever, the company is not a charity.

There are quite a few softwares that can be used by the second mobile phone and the computer at the same time, but those with more complicated functions can only be used on the computer, such as Kingdee. If you want to use your mobile phone and computer at the same time, you need to find a lightweight invoicing software, just like Wechat business Photo Album. Your mobile phone and computer can be used at the same time, and all the functions are available.