The option for 2-Sided Printing (Windows) or Two-Sided Printing Settings (Mac) is gray or not available. What should I do?

Make sure you use a paper type and size that is supported for this feature. Automatic double-sided printing is only available if you select plain paper and one of these paper sizes in the printer software:

• Letter (8.5 × 11 inches [216 × 279 mm])
• A4 (8.3 × 11.7 inches [210 × 297 mm])

Note: Automatic double-sided printing is not supported on glossy, thick, and certain matte papers.