You had a price, a lender and a plan, and then the appraisal landed under the number and the loan shrank with it. This is one of the most common ways a commercial deal stalls in British Columbia, and it is usually fixable, though rarely by arguing with the appraiser.

Lenders size against the lesser of purchase price and appraised value. When the appraisal lands under the price, the loan follows it down, and the difference has to come from somewhere else.
On income producing property the appraisal is usually an income approach. That means a low value is often a view on your rents, your vacancy assumption or your expenses rather than a view on the building itself. It is worth reading the report closely to find out which. You can also size the loan against the new value before you decide anything.
A reconsideration of value succeeds on new facts, not on disagreement. Comparable sales the appraiser did not have. An error in the rent roll. A lease signed after the inspection date. Square footage measured wrong. Capital work that is not reflected in the report.
It goes through the lender who ordered the appraisal, never directly to the appraiser. A calm submission of documents does far more than an argument about the number.
Put in more equity. The simplest answer, and the cheapest, where the cash exists.
Add a second mortgage. A charge behind the first works, but it costs meaningfully more than the first mortgage and should be treated as short term. Of the four routes this is the most expensive.
Reopen the price. The appraisal is evidence, and a vendor who wants to close will often listen to it.
Change lender. Move to a lender whose sizing is driven by something other than that appraised value. What lenders look for is set out on the commercial mortgage requirements page.
If the appraisal is right and the price was wrong, the appraisal has just saved you from overpaying.
Paying the difference in cash to force a deal that the market does not support is how people end up trapped in a building they cannot refinance.
A senior broker will tell you whether the value is worth challenging, and what the deal looks like if it is not.