Signup form labels don’t match input fields

The labels in your signup form refer to IDs that do not exist. You need to change the relevant code in class-sendpress-sc-signup.php to this:

<?php if( filter_var($display_firstname, FILTER_VALIDATE_BOOLEAN)  ): ?>
						<p name="firstname">
							<?php if( !$label ): ?>
								<label for="sp_firstname"><?php echo $firstname_label; ?>:</label>
							<?php endif; ?>
							<input type="text" id="sp_firstname" class="sp_firstname" <?php if($label){ echo 'placeholder="'.$firstname_label.'"';}?> value=""  name="sp_firstname" />
						</p>
					<?php endif; ?>

					<?php if( filter_var($display_lastname, FILTER_VALIDATE_BOOLEAN) ): ?>
						<p name="lastname">
							<?php if( !$label ): ?>
								<label for="sp_lastname"><?php echo $lastname_label; ?>:</label>
							<?php endif; ?>
							<input type="text" id="sp_lastname" class="sp_lastname" <?php if($label){ echo 'placeholder="'.$lastname_label.'"';}?>  value="" name="sp_lastname" />
						</p>
					<?php endif; ?>

					<p name="email">
						<?php if( !$label ): ?>
							<label for="sp_email"><?php echo $email_label; ?>:</label>
						<?php endif; ?>
						<input type="text" id="sp_email" class="sp_email" <?php if($label){ echo 'placeholder="'.$email_label.'"';}?> value="" name="sp_email" />
					</p>