Ambassadors receive their reward tokens from whatever remains of the 3.6m PRIME budget established in the Incubation stage for governance. This budget was established in PDP 001. From the proposal:
In the Incubation stage, Prime may issue a maximum of 3.6m PRIME as rewards, as determined by the litepaper. At the initialization of the Growth phase, these rewards will be foremost issued to Incubation contributors in vesting contracts, and the remainder of the unassigned PRIME will be distributed to its ecosystem governors [ambassadors] in vesting contracts in exchange for their good governance.
Contributors will receive their reward tokens from the contributor reward portion of the overall budget distribution, or 14.5M PRIME tokens. Note that the following rewards matrices may stack REP accumulated as ambassadors or contributors with REP earned from locked PRIME, up to a maximum ceiling of 500 REP for a given individual, or 1000 REP for a given organization: