Can I apply for multiple round-trip endorsement of Hong Kong and Macao Pass in Hangzhou with the invitation letter from Hong Kong company?

You can go back and forth many times. According to the policy of China government, official website shows that applicants need to live permanently in Hangzhou and meet the following conditions: holding a valid ordinary passport, a valid Hong Kong permanent identity card or a valid Macao Special Administrative Region resident identity card, obtaining an invitation letter from a Hong Kong company and being certified by the Immigration Department of the Hong Kong SAR Government. Hong Kong and Macao Pass can be divided into single round-trip endorsement and multiple round-trip endorsement. The validity period is half a year and one year respectively. In the application process, the applicant needs to provide sufficient materials to prove that he will be endorsed after being approved by the public security organ.