Enhance Open Source CRM with integration to Quickbooks with QB SDK and billing features

PHP programmers only. We want to enhance an existing CRM (Developer suggests an existing Open Source system) to integrate with QB via their SDK so that all billing and account reconciliation occurs in QB. The CRM will be the only line of contact with the customer. Customers will be able to be created online by themselves or the company. Services ordered through the CRM. CRM will be able to bill these services on a recurring basis (hourly, daily, weekly, monthly, yearly) and then let QB charge the account and credit the account. CRM will track implementation all the way through cancellation and disconnection of the services. CRM will be responsible for customer contact (your payment didn't go through, here is your statement, etc). CRM will be able to handle annual escalations of service fees (every X periods it goes up by 4% for example). CRM needs to be able to reconcile transactions between its own records and QBs (for example, if QB didn't charge or wasn't able to charge an account, CRM needs to flag it as an error. If the balances don't match, etc). During implementatation stage of an order, certain details of the order will need to be stored by the CRM (some hidden from the customer, some shared). Various emails of communications (templates provided by us) will need to be generated to update the customer. All emails need to be saved in the database to be able to be re-sent on demand. Standard password recovery and 2FA functions. Certain approvals between customer order and implementation (various groups have privileges to approve or edit the order before fully accepting it). System will need to integrate with our external document signature software including document storage. Milestones to be negotiated in direct conversations with applicants. suggested milestones: MS1) Approve OSS CRM and validate QB integration $750 - 2 weeks MS2) Create features for user account creation/ordering. $750 - 2 weeks MS3) Demonstrate successful integration with e-signature software. $750 - 2 weeks MS4) Demonstrate complete order flow from account creation, authorizations, document signing, implementation and recurring billing with escalations. $750 - 2 weeks Milestones paid after code is validated. All code is submitted through our private Gitlab. We will provide a development environment accessible by SSH/Web.