THCA is not federally banned in the U.S. Department of State, but their sale or possession could be prosecuted under the Federal Analogs Act. You can ingest THCA by smoking certain varieties of marijuana, ingesting marijuana products specific to THCA and cannabis extracts, such as crystalline THCA, and even eating raw cannabis leaves or putting them in a smoothie. For example, I recently consulted a certificate of analysis (COA) of a THCA flower that showed 25% THCA and 0.18% D9. Because the THCA flower does not exceed this figure, certain states, such as North Carolina, can legally sell THCA.
While THCa doesn't have an intoxicating effect when ingested, the reason marijuana smokers accept this total THC profile is that THCA converts to D9 when heated in a chemical process called decarboxylation. The number 0.877 is used because it is the percentage of THCA that remains after decarboxylation, the process in which heat, time, or both convert THCA to THC.