WP_query taxonomy issue

I don't know if you can help me with issues that aren't to do with your plugins or themes, but from what I read on your website you'll help with pretty much anything WP related.

I have what's probably an incredibly simple issue, however I'm having trouble passing parameters through my query. I'm basically trying to pass the terms as a variable to the tax query however it doesn't work, if i manually write in the terms, it works fine, I don't understand why the variable doesn't, because if I echo the variable into the page, it outputs exactly what i type in manually.

Are you able to assist with this? If so my query is below:

<?php 

			$terms = the_field('product_groups');
			echo $terms;

			$args = array(
				'post_type' => 'product',
				'posts_per_page' => '-1',
				'order_by' => 'date', // it's also default
				'order' => 'DESC', // it's also default
				'tax_query' => array(
					array(
						'taxonomy' => 'product-group',
						'terms' => array( $terms )
					)
				)
			);

			// the query
			$the_query = new WP_Query( $args ); ?>

			<?php if ( $the_query->have_posts() ) : ?>

				<!-- the loop -->
				<?php while ( $the_query->have_posts() ) : $the_query->the_post(); ?>
					<h2><?php the_title(); ?></h2>
				<?php endwhile; ?>
				<!-- end of the loop -->

				<?php wp_reset_postdata(); ?>

			<?php else : ?>
				<p><?php _e( 'Sorry, no posts matched your criteria.' ); ?></p>
			<?php endif; ?>

Like i said, if i echo $terms into the page, it gives me '10, 12, 11', if i replace the variable in the query with that, it works fine, but with the variable, nothing.