Self Hosted / Whitelabel licence query

Just a quick query on the Self hosted / whitelabel licence ($20/year)
Is this licence only to be used for a single installation / domain
or can it be used on multiple domains ie and,

The reason im asking is i am wanting to keep the client link to view the invoices the same as the domain name for each company, instead of setting up all 3 companies on the same installation where they will all be pointed to the same domain to view the invoice

The license is intended for use on a single installation/domain

Thanks Hillel