Unable to claim the BC Sales tax credit although eligible. I click the box, but it does not show up as claimed on the next menu but "BC tax reduction credit" does?

The BC sales tax credit can show as zero depending on how much income you make. See the example below:

The maximum credit is $75 for the taxpayer and $75 for his or her spouse or common-law partner. If you’re single, the credit is reduced by 2% of your net income over $15,000. If you have a cohabiting spouse or common-law partner, the credit is reduced by 2% of your family net income over $18,000. The credit is eliminated entirely when your income reaches $18,750 for individuals, and $25,500 for spouses combined.

For example, John and Sharon make a combined income of $27,000. The form requires them to deduct $18,000 as a couple, leaving $9,000. Their total claim is 2 x $75 = $150 and is reduced by 2 percent of the amount that their combined income exceeds $18,000 ($9,000 x 2 percent = $180). Note that a negative amount results in a claim of zero.

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